Brush-like layer

Calculations from SCF theory of the mixed layer structure, and of the interaction potential for a pair of mixed layers as a function of interlayer separation, suggest that the mixed layer has a heterogeneous morphology perpendicular to die interface (Parkinson et al., 2005). This localized segregation arises from the excluded volume interaction between spaced-out casein chains and the dense brush-like layer that was invoked in the simple SCF model to represent the p-lactoglobulin adsorbed monolayer. 

Section 4 focuses on the segregation of diblock copolymers admixed to homopolymer matrices. The copolymers form brush-like layers composed of chains attached by their anchor blocks to the external interface. Similar dou-... 

Diblock copolymers A-N immersed in a homopolymer P matrix segregate to its interfaces. One of the copolymer blocks ( anchor moiety A) selectively attaches to the interface while the other ( buoy block N) dangles out to form a brush like layer, providing a simple means for the realization of polymer brushes (see Fig. 33). 

An extended brush-like layer is formed for the zwitterionically terminated polystyrene and comparison of force-distance curves before and after oscillatory motion showed that they were not displaced by the lubrication forces. These force-distance curves showed that the two brush-like layers interact at distances of about 2500 A. Above this separation, values of G scale with D in precisely the same manner both in the presence and in the absence of tethered polymer. The slopes of these lines, moreover, gave a viscosity (j/o) that agreed with the bulk viscosity of toluene. For the tethered pol)nner the line through these large separation data has an x axis intercept that corresponds closely to twice the polymer layer s thickness. Hence, in this region the shear plane in the system has shifted by a distance of 2Lh (Lr is hydrod5mamic layer thickness equilibrium layer thickness) and thus equation (3.4.13) becomes... 

Figure 6.6. Reduced force as a function of reduced distance for the close approach of two brush-like layers. The data points are for a number of 2-vinyl pyridine/isoprene and 2-vinyl pyridine/styrene diblocks with various degrees of polymerisation. The solid line is the prediction of PTH theory with — 0.58, the short dashed line PTH theory with = 1 and the long dashed line the prediction of self-consistent field theory. After Watanabe and Tirrell (1993).

Figure 8.6. A schematic surface pressure isotherm for a polymer at the air/water interface that forms a brush-like layer in the aqueous phase.

Figure 8.7. A schematic volume fraction profile for a brush-like layer at an interface. 0s and 0OO are the surface volume fraction and equilibrium bulk volume fi action of the polymer, respectively.

While the thiol groups were found to be suitable for gold surfaces, cyclic disulfide systems were preferred. The spacer length was also found to be a critical parameter, as very short linkers produce ill defined layers that improve considerably with increased length. On the other hand, highly organized layers tend to limit the number of bacteria bound to them, whereby extended spacers form a brush -like surface coat and increase bacterial trapping ... 

Amylose brushes (a layer consisting of polymer chains dangling in a solvent with one end attached to a surface is frequently referred to as a polymer brush) on spherical and planar surfaces can have several advantageous uses, such as detoxification of surfaces etc. The modification of surfaces with thin polymer films is widely used to tailor surface properties such as wettability, biocompatibility, corrosion resistance, and friction [142-144]. The advantage of polymer brushes over other surface modification methods like self-assembled monolayers is their mechanical and chemical robustness, coupled with a high degree of synthetic flexibility towards the introduction of a variety of functional groups. 

Figure 8.5 Interaction potential for model whey protein layer consisting of densely packed brush-like tethered chains with small a fraction of the whev protein replaced by p-casein chains as represented by a copolymer model. The energy A d) calculated from SCF theory is plotted as a function of surface-surface separation d A, no p-casein B, 2.5% p-casein C, 5% p-casein D, 5% p-casein alone (without whey protein layer). Potentials A, B and D imply that the emulsion system is flocculated potential C implies a stable emulsion state. Reproduced from Dickinson (2006b) with permission.

Many decapods have very dense, brush-like arrays of olfactory sensilla and this more or less dense packing of aesthetascs inhibits water flow between them. Thus, the aesthetascs are embedded in a viscous boundary layer of water. Exchange of the boundary layer water is achieved by flicking, an intermittent powerful beat of the entire antennula that allows rapid odor access to the animal s aesthetasc tufts by splaying out the aesthetasc sensilla and substituting the water lodged there with new water (Schmitt and Ache 1979 Koehl, Chap. 5). 

Figure 3.35. G as a function of the surface separation for two surfaces with brush-like polystyrene layers immersed in toluene. The dashed line corresponds to data in the absence of the polymer (and also after incubation in the presence of a polymer with no functional ends). The solid line has a slope of j/q. After Klein et al (1993).

In the above discussion we were concerned with adding flexible-chain polymers to dispersions. A particularly interesting case is that of polymers grafted at one end onto the particle surfaces. For high enough grafting densities, this produces a brush-like effect on the surface (cf. Fig. 3.15). Now the chains are stretched out and the thickness of the layer is... 

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